Liquid crystal display

ABSTRACT

A liquid crystal display with better visibility and transmittance. The liquid crystal display includes a first plate having a first field-generating electrode, disposed in a pixel area on an insulating substrate, comprising a plurality of sub-electrodes which are separated from each other by a predetermined distance and arranged parallel to each other, and a connecting electrode electrically connecting the sub-electrodes. An alignment film that is rubbed in a first direction covers a first field-generating electrode and an alignment film that is rubbed in a second direction covers a second field-generating electrode to achieve a predetermined orientation of the liquid crystals when no field is applied and more uniform rotation of the liquid crystal molecules when a field is applied.

REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No.10-2005-0071898 filed on Aug. 5, 2005 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a liquid crystal display having bettervisibility and light transmittance.

DESCRIPTION OF THE RELATED ART

The liquid crystal display (“LCD”), is a flat panel display thatincludes two plates having a plurality of electrodes with a liquidcrystal layer between them. Voltages applied to the electrodes rearrangethe liquid crystal molecules thereby displaying images by varying theamount of transmitted light. In the LCD, thin film transistors are usedas switching elements for controlling the application of picture signalsto the electrodes.

The vertical alignment (VA) mode LCD aligns the long axes of the LCmolecules perpendicularly to the plates in absence of electric field.The VA mode LCD offers a wide reference viewing angle and large contrastratio. The wide viewing angle can be realized by forming cutouts orprotrusions in each field-generating electrode so that the reultantfringe field more uniformly distributes the tilt angles of the liquidcrystal molecules. The patterned vertically aligned (PVA) mode offorming cutout patterns in electrodes is a recognized way of achieving awide viewing angle and is an alternative to using the horizontalelectric field mode such as the in-plane switching (IPS) mode or thefringe field switching (FFS) mode.

However, the PVA-mode liquid crystal display shows a lateral gamma curvedistortion so that the front gamma curve and the lateral gamma curve donot agree to each other resulting in lower left and right visibilitythan the twisted nematic (TN)-mode liquid crystal display. For example,PVA-mode liquid crystal displays having cutouts as domain-definingmembers show images that become bright and white toward the lateralside, and in the worst case, the luminance difference between high graysvanishes such that the images cannot be perceived.

SUMMARY OF THE INVENTION

The present invention provides a liquid crystal display with bettervisibility, light transmittance, which has high process efficiency andcan prevent electric field distortion.

According to an aspect of the present invention, there is provided aliquid crystal display including a first plate having a firstfield-generating electrode disposed in a pixel area of on insulatingsubstrate, comprising a plurality of sub-electrodes which are separatedfrom each other by a predetermined distance and arranged parallel toeach other, and a connecting electrode electrically connecting thesub-electrodes, and a first alignment film covering the firstfield-generating electrode said first alignment film having been rubbedin a first direction, a second plate having a second field-generatingelectrode disposed on an insulating substrate, and a second alignmentfilm covering the second field-generating electrode said secondalignment film having been rubbed in a second direction, and a liquidcrystal layer interposed between the first plate and the second plate.

According to another aspect of the present invention, there is provideda liquid crystal display having a first plate including a firstfield-generating electrode disposed in a pixel area of an insulatingsubstrate, and a first alignment film covering the firstfield-generating electrode said first alignment film having been rubbedin a first direction, a second plate having a second field-generatingelectrode, disposed on an insulating substrate, said secondfield-generating electrode having a plurality of openings formedparallel to each other in an area corresponding to the pixel area of thefirst plate, and a second alignment film covering the secondfield-generating electrode said second alignment film having been rubbedin a second direction, and a liquid crystal layer interposed between thefirst plate and the second plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a layout of a liquid crystal display according to a firstembodiment of the present invention;

FIG. 2 is a sectional view taken along a line II-II′ of FIG. 1;

FIGS. 3 and 4 are respectively schematic plan and sectional viewsillustrating the arrangement of liquid crystal molecules when a thinfilm transistor of the liquid crystal display according to the firstembodiment of the present invention is in an “OFF” state;

FIG. 5 is a schematic sectional view illustrating the arrangement ofliquid crystal molecules when a thin film transistor of the liquidcrystal display according to the first embodiment of the presentinvention is in an “ON” state;

FIG. 6 is a layout of a liquid crystal display according to a secondembodiment of the present invention;

FIG. 7 is a sectional view taken along a line VII-VII′ of FIG. 6;

FIGS. 8 and 9 are respectively schematic plan and sectional viewsillustrating the arrangement of liquid crystal molecules when a thinfilm transistor of the liquid crystal display according to the secondembodiment of the present invention is in an “OFF” state;

FIG. 10 is a schematic sectional view illustrating the arrangement ofliquid crystal molecules when a thin film transistor of the liquidcrystal display according to the second embodiment of the presentinvention is in an “ON” state;

FIG. 11 is a layout of a liquid crystal display according to a thirdembodiment of the present invention;

FIG. 12 is a sectional view taken along a line XII-XII′ of FIG. 11;

FIGS. 13 and 14 are respectively schematic plan and sectional viewsillustrating the arrangement of liquid crystal molecules when a thinfilm transistor of the liquid crystal display according to the thirdembodiment of the present invention is in an “OFF” state;

FIG. 15 is a schematic sectional view illustrating the arrangement ofliquid crystal molecules when a thin film transistor of the liquidcrystal display according to the third embodiment of the presentinvention is in an “ON” state;

FIG. 16 is a layout of a liquid crystal display according to a fourthembodiment of the present invention;

FIG. 17 is a sectional view taken along a line XVI-XVI′ of FIG. 16;

FIGS. 18 and 19 are respectively schematic plan and sectional viewsillustrating the arrangement of liquid crystal molecules when a thinfilm transistor of the liquid crystal display according to the fourthembodiment of the present invention is in an “OFF” state;

FIG. 20 is a schematic sectional view illustrating the arrangement ofliquid crystal molecules when a thin film transistor of the liquidcrystal display according to the fourth embodiment of the presentinvention is in an “ON” state; and

FIG. 21 is a sectional diagram illustrating equipotential lines formedin the “ON” state of a thin film transistor of a liquid crystal displayaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Advantages and features of the present invention and methods ofaccomplishing the same may be understood more readily by reference tothe following detailed description of preferred embodiments and theaccompanying drawings. Like reference numerals refer to like elementsthroughout the specification.

Hereinafter, a liquid crystal display according to a first embodiment ofthe present invention will be described with reference to FIGS. 1 and 2.FIG. 1 is a layout of a liquid crystal display according to a firstembodiment of the present invention and FIG. 2 is a sectional view takenalong a line II-II′ of FIG. 1.

The liquid crystal display includes a first plate 100, a second plate200 facing the first plate 100, and a liquid crystal layer 300interposed between the first plate 100 and the second plate 200,including liquid crystal molecules 310 aligned horizontally with respectto the first and second plates 100, 200.

First, with respect to the first plate 100, a pixel electrode 182 madeof transparent conductive oxide such as an indium tin oxide (ITO) orindium zinc oxide (IZO) is disposed on a substrate 110 made of atransparent insulating material such as glass. The pixel electrode 182is a field-generating electrode and includes a plurality ofsub-electrodes 182 a parallel to and separated from each other by apredetermined distance and a connecting electrode 182 b electricallyconnecting the sub-electrodes 182 a. The pixel electrode 182 isconnected to a thin film transistor to receive an image signal voltage.The thin film transistor is connected to a gate line 122 responsible forscan signal transmission and a data line 162 responsible for imagesignal transmission, and turns on/off the pixel electrode 182 accordingto a scan signal. An alignment film is disposed on the substrate 110having thereon the pixel electrode 182. Alignment film 190 allows theliquid crystal molecules 310 of the liquid crystal layer 300 to behorizontally aligned in a voltage-off state.

In addition, with respect to the second plate 200, a black matrix 220for preventing light leakage, a color filter 230 composed of red, green,and blue components, and a common electrode 270 which is afield-generating electrode made of transparent conductive oxide such asITO or IZO are formed on a lower surface of a substrate 210 made of atransparent insulating material such as glass.

An alignment film 280 is disposed on substrate 210 having thereon commonelectrode 270. Alignment film 280 allows the liquid crystal molecules310 of the liquid crystal layer 300 to be horizontally aligned in avoltage-off state.

A liquid crystal display according to the first embodiment of thepresent invention will be described in more detail.

First, with respect to the first plate 100, gate wires formed on thesubstrate 110 include the gate line 122 extending in a transversedirection, a gate pad 124 connected to an end of the gate line 122 toreceive a gate signal from an external device and transmit the receivedgate signal to the gate line 122, and a gate electrode 126 of a thinfilm transistor which is connected to the gate line 122 and formed in aprotrusion shape. Here, the gate wires may have a single layeredstructure including a conductive layer made of an Al containing metalsuch as Al or an Al alloy, or a multi-layered structure (not shown)including another layer made of, particularly, a material that showsphysically, chemically and electrically good contact characteristicswith respect to ITO or IZO, such as Cr, Ti, Ta, Mo or an alloy thereof,formed on the conductive layer.

A gate insulating film 130 made of silicon nitride (SiNx), etc. isdisposed on the substrate 110 and the gate wires.

Data wires including a source electrode 165 and a drain electrode 166are disposed on the gate insulating film 130. The data wires extendingalong a longitudinal direction intersect the gate wires, defining apixel region shaped of, for example, a rectangle. The data wires includea data line 162, a source electrode 165 as a branch of the data line162, a drain electrode 166 formed in the neighbourhood of the sourceelectrode 165 and a data pad 168 formed at an end of the data line 162.Like the gate wires, the data line 162, the source electrode 165, thedrain electrode 166, and the data pad 168 may have a single layeredstructure including a conductive layer made of an Al containing metalsuch as Al or an Al alloy, or a multi-layered structure (not shown)including another layer made of, particularly, a material that showsphysically, chemically and electrically good contact characteristicswith respect to ITO or IZO, such as Cr, Ti, Ta, Mo or an alloy thereof,formed on the conductive layer.

A semiconductor layer 140 defining a channel region of a thin filmtransistor is formed in an island shape below the source electrode 165and the drain electrode 166. In addition, ohmic contact layers 155 and156 are formed of, for example, silicide or n+ hydrogenated silicondoped with a high concentration of n-type impurities, on thesemiconductor layer 140 to reduce contact resistance between thesource/drain electrodes 165 and 166 and the semiconductor layer 140.

A passivation layer 170 made of an inorganic insulating material such assilicon nitride or an organic insulating material such as resin isformed on the data wires. Contact holes 177 and 178 exposing the drainelectrode 166 and the data pad 168, respectively, are formed on thepassivation layer. In addition, a contact hole 174 is formed on thepassivation layer through the gate insulating layer 130 to expose thegate pad 124.

A pixel electrode 182 electrically connected to the drain electrode 166via the contact hole 177 is disposed on the passivation layer. The pixelelectrode 182 includes the plurality of the sub-electrodes 182 a and theconnecting electrode 182 b connecting the sub-electrodes 182 b. Thesub-electrodes 182 b of the pixel electrode 182 may have a predeterminedshape, for example, stripes formed in parallel with longer sides of thepixel area. In this case, a width of each of the sub-electrodes 182 aand a distance between the sub-electrodes 182 b depend on opticalproperties of an LCD. For example, a width of each of the sub-electrodes182 a may be approximately 6 μm or less, and a distance between thesub-electrodes 182 a may range from approximately 4 to approximately 14μm. If the width of each of the sub-electrodes 182 a is 4 μm, thedistance between the sub-electrodes 182 a may be approximately 11 μm.The connecting electrode 182 b of the pixel electrode 182 is formed toelectrically connect the respective sub-electrodes 182 a to each other.The connecting electrode 182 b may be formed by connecting therespective sub-electrodes 182 a to each other at either side or bothsides of the sub-electrodes 182 a or at the central portion ofsub-electrodes 182 a, and a connecting portion of the respectivesub-electrodes 182 a is not particularly limited. The pixel electrode182 applied with a pixel voltage generates an electric field togetherwith common electrode 270 of the second plate 200, thereby determiningthe directions of the liquid crystal molecules 310 of the liquid crystallayer 300 between pixel electrode 182 and common electrode 270.

An auxiliary gate pad 184 and an auxiliary data pad 188 connected to agate pad 124 and a data pad 168 via the contact holes 174 and 178,respectively, are also disposed on the passivation layer. The auxiliarygate pad 184 and the auxiliary data pad 188 complement adhesions toexternal circuit devices and protect the gate pad 124 and the data pad168. The auxiliary gate pad 184 and the auxiliary data pad 188 may bemade of ITO or IZO.

As referenced above, alignment film 190 is disposed on the substrate 110having the pixel electrode 182. Alignment film 190 is ahorizontal-alignment film that allows the liquid crystal molecules 310of the liquid crystal layer 300 to be aligned horizontally with respectto the substrate 110 in a voltage-off state. An alignment film may beused to allow the liquid crystal molecules 310 to have a pre-tilt angleof, for example, 0.5 to 3 degrees, to prevent the formation of two ormore domains in a voltage-on state. In addition, alignment film 190 isrubbed so that the liquid crystal molecules 310 of the liquid crystallayer 300 are aligned at an angle of α with respect to thesub-electrodes 182 a in a voltage-off state. Here, the angle of α may bedetermined by the known optical properties of the liquid crystaldisplay, and may be an arbitrary angle except 0 and 90 degrees. Forexample, the angle of α may be an angle in the range between 60 and 85degrees.

The second plate 200 will next be described. A black matrix 220 forpreventing light leakage is disposed on the surface of substrate 210facing the first plate 100. Color filter 230 composed of red, green, andblue components is disposed on black matrix 220. An overcoat layer 250is disposed on color filter 230 to planarize the stepped surface of thecolor filter.

Common electrode 270 is disposed on overcoat layer 250. Common electrode270 may be made of, for example, a transparent conductive material suchas ITO or IZO.

Alignment film 280 is disposed on substrate 210 having thereon commonelectrode 270. Alignment film 280 is rubbed so that the liquid crystalmolecules 310 are aligned horizontally with respect to the surface ofsubstrate 210 at a pretilt angle of, for example, 0.5 to 3 degrees, in avoltage-off state. Alignment film 280 is rubbed in the oppositedirection to the rubbing direction of alignment film 190 of the firstplate 100, i.e., so that the rubbing direction of the alignment film andthe rubbing direction of the alignment film form an angle of 180degrees. For example, alignment film 190 of the first plate 100 andalignment film 280 of the second plate 200 may be rubbed at an angle ofα under the condition that the rubbing direction of alignment film 190and the rubbing direction of alignment film 280 form an angle of 180degrees. The angle of α may depend upon settings in optical propertiesof the LCD and may be an arbitrary angle except 0 and 90 degrees, forexample, an angle in the range between 65 and 80 degrees.

The liquid crystal layer 300 including the liquid crystal molecules 310is interposed between the above-described thin filmtransistor-containing first plate 100 and color filter-containing secondplate 200. The liquid crystal molecules 310 are horizontally alignedbetween the first plate 100 and the second plate 200, and have negativedielectric anisotropy (Δε<0), i.e., the long axes of the liquid crystalmolecules 310 are aligned vertically with respect to an applied electricfield. The liquid crystal molecules 310 are driven according to theon/off state of pixels in such a way that their long axes aresubstantially parallel to the surfaces of the substrates 110 and 210.

Next, the arrangement of the liquid crystal molecules 310 in the on/offstate of a thin film transistor of the liquid crystal display accordingto the illustrative embodiment will now be described with reference toFIGS. 2 through 5. FIGS. 3 and 4 are respectively schematic plan andsectional views illustrating the arrangement of liquid crystal moleculeswhen a thin film transistor of the liquid crystal display according tothe first embodiment of the present invention is in an “OFF” state, andFIG. 5 is a schematic sectional view illustrating the arrangement ofliquid crystal molecules when a thin film transistor of the liquidcrystal display according to the first embodiment of the presentinvention is in an “ON” state.

First, referring to FIGS. 2 through 4, in the “OFF” state of the thinfilm transistorr, liquid crystal molecules 310 between common electrode270 and the underlying sub-electrodes 182 a are aligned parallel to therubbing direction of the horizontal alignment films so that their longaxes are inclined at a pretilt angle of 0.5 to 3 degrees with respect tosubstrates 110 and 210. For example, alignment film 190 of the firstplate 100 is rubbed such that it has a tilt angle of 60° to 85° withrespect to the sub-electrode 182 a and alignment film 280 of the secondplate 200 is rubbed such that it has a tilt angle of 180° with respectto the rubbing direction of alignment film 190 of the first plate 100.In the latter case, the long axes of the liquid crystal molecules 310are arranged at an angle of approximately 60 to 85° with respect to thesub electrode 182 a.

Next, referring to FIGS. 2 and 5, when the thin film transistor isturned-on and an image signal is applied to the pixel electrode 182, anelectric field is generated between the first plate 100 and the secondplate 200. At this time, the central portions of sub-electrodes 182 adirect a vertical electric field toward corresponding portions of commonelectrode 270. However, the side portions of sub-electrodes 182 a directan outwardly curved horizontal electric field. The liquid crystalmolecules 310 adjacent to the alignment films 190 and 280 maintain theiroriginal alignments because of the anchoring energy on the alignmentfilms 190 and 280. The liquid crystal molecules 310 disposed in thecentral area of liquid crystal layer 300 are rotated so that their longaxes are aligned vertically with respect to the applied electric fielddue to their negative dielectric anisotropy. In a voltage-off state, theliquid crystal molecules 310 are tilted at a predetermined angle withrespect to the sub-electrodes 182 a by rubbing of the alignment films190 and 280. In a voltage-on state, the liquid crystal molecules 310 areuniformly rotated in the same direction based on the tilted angle.

Pixel electrode 182 of the first plate 100 includes a plurality of thesub-electrodes 182 a having a predetermined shape, whereas commonelectrode 270 of the second plate 200 is not subjected to patterning.This offers process simplicity, compared to patterning thefield-generating electrodes of both he first and second plates. Also,there is no need to use a separate conductive polarization plate forpreventing electrostatic marks or abnormal domains that may be caused bycommon electrode patterning of an upper plate, leading to cost-saving.Furthermore, since common electrode 270 is not subjected to patterning,there is no misalignment between the pixel electrode 182 of the firstplate 100 and common electrode 270 of the second plate 200, therebyavoiding distortion of the electric field. Still furthermore, an overlaparea between the pixel electrode 182 and common electrode 270 isreduced, thereby leading to low liquid crystal capacitance. In addition,since the liquid crystal molecules 310 are tilted at a predeterminedangle with respect to the sub-electrodes 182 a in a voltage-off state,they can be uniformly rotated in the same direction in a voltage-onstate. Therefore, the liquid crystal display of this embodiment is freefrom textures that are caused between liquid crystal molecules rotatingin different directions, thereby leading to no abnormal domains.Further, since the liquid crystal molecules 310 disposed at sideportions of the sub-electrodes 182 a and between adjacent ones of thesub-electrodes 182 a are aligned vertically with respect to a horizontalelectric field, transmittance equal to or greater than a PVA-mode isobtained. Still further, the liquid crystal display of this embodimentshows maximal transmittance compared to another liquid crystal displaysusing liquid crystal molecules with higher dielectric anisotropy and thesame voltage, and the in-plane movement of the directors of the liquidcrystal molecules 310 increases, thereby ensuring better visibility.

Hereinafter, a liquid crystal display according to a second embodimentof the present invention will be described with reference to FIGS. 6 and7. FIG. 6 is a layout of a liquid crystal display according to thesecond embodiment of the present invention, and FIG. 7 is a sectionalview taken along a line VII-VII′ of FIG. 6.

The liquid crystal display of the second embodiment is the same as theliquid crystal display of the first embodiment of the present inventionexcept that alignment film 190 of the first plate 100 and alignment film280 of the second plate 200 are rubbed at an angle of 90 degrees withrespect to the longer side of a pixel area under the condition that therubbing direction of alignment film 190 of the first plate 100 and therubbing direction of alignment film 280 of the second plate 200 form anangle of 180 degrees, and sub-electrodes 182 a are formed parallel toeach other in a state in which they are inclined at a predeterminedangle, e.g., an angle from 60 to 85 degrees, with respect to the rubbingdirection of the alignment film of the first plate 100. Thus, therepeated descriptions will be omitted.

Next, the liquid crystal molecule arrangement in the on/off state of athin film transistor of the liquid crystal display according to thesecond embodiment will now be described with reference to FIGS. 7through 10. FIGS. 8 and 9 are respectively schematic plan and sectionalviews illustrating the arrangement of liquid crystal molecules when athin film transistor of the liquid crystal display according to thesecond embodiment of the present invention is in an “OFF” state, andFIG. 10 is a schematic sectional view illustrating the arrangement ofliquid crystal molecules when a thin film transistor of the liquidcrystal display according to the second embodiment of the presentinvention is in an “ON” state.

First, referring to FIGS. 7 through 9, with respect to the liquidcrystal molecule arrangement in an “OFF” state thin film transistor, thesub-electrodes 182 a are formed parallel to each other in a state inwhich they are inclined at a predetermined angle, e.g., at an angle of60 to 85 degrees with respect to the rubbing direction of the alignmentfilm of the first plate 100 rubbed at an angle of 90 degrees withrespect to the longer side of the pixel area. Liquid crystal molecules310 between a pixel electrode 182 including the sub-electrodes 182 a anda common electrode 270 are aligned parallel to the rubbing direction ofthe horizontal alignment films in a state in which their long axes areinclined at a pretilt angle of 0.5 to 3 degrees with respect to thesurfaces of first and second substrates 110 and 210. That is, the longaxes of the liquid crystal molecules 310 are arranged at an angle ofapproximately 90° with respect to a longer side of the pixel area.Consequently, the along axes of the liquid crystal molecules 310 arearranged at a tilt angle (α) of approximately 60 to approximately 85°with respect to the sub electrode 182 a.

Next, referring to FIGS. 7 and 10, with respect to the arrangement ofthe liquid crystal molecules 310 in an “ON” state thin film transistor,when the thin film transistor is turned-on and an image signal isapplied to the pixel electrode 182, an electric field is generatedbetween the first plate 100 and the second plate 200. At this time, asdescribed above in the liquid crystal molecule arrangement of the liquidcrystal display of the previous embodiment, in central portions of thesub-electrodes 182 a, there is generated a vertical electric fielddirecting toward portions of common electrode 270 corresponding to thecentral portions of the sub-electrodes 182 a. On the other hand,referring to FIG. 21 a horizontal electric field which is not directedto common electrode 270 but is curved outward is generated in sideportions(a, b) of the sub-electrodes 182 a. The liquid crystal molecules310 adjacent to the alignment films 190 and 280 maintain their originalalignments, whereas the liquid crystal molecules 310 disposed in thecentral area of the liquid crystal layer 300 are rotated so that theirlong axes are aligned vertically with respect to an applied electricfield due to the negative dielectric anisotropy. At this time, theliquid crystal molecules 310 are uniformly rotated in the same directionbased on a tilted angle created by rubbing of the alignment films 190and 280.

In the liquid crystal display of this embodiment, like the liquidcrystal display of the previous embodiment, common electrode 270 is notsubjected to patterning. Therefore, process simplicity and cost-savingeffect are obtained, and electric field distortion caused by amisalignment between the first plate 100 and the second plate 200 doesnot occur. Furthermore, an overlap area between the pixel electrode 182and common electrode 270 is minimized, thereby ensuring low liquidcrystal capacitance. Still furthermore, the liquid crystal molecules 310are uniformly rotated in the same direction, and thus the formation oftextures and thus abnormal domains is excluded. In addition,transmittance equal to or greater than a PVA-mode is obtained, and evenmore, the liquid crystal display of the second embodiment shows maximaltransmittance compared to another liquid crystal displays using liquidcrystal molecules with higher dielectric anisotropy and the samevoltage, and the in-plane movement of the directors of the liquidcrystal molecules 310 is increased, thereby ensuring better visibility.

Hereinafter, a liquid crystal display according to a third embodiment ofthe present invention will be described with reference to FIGS. 11 and12.

FIG. 11 is a layout of a liquid crystal display according to a thirdembodiment of the present invention, and FIG. 12 is a sectional viewtaken along a line XII-XII′ of FIG. 11.

A first plate 100 of the liquid crystal display of the third embodimentis the same as the first plate 100 of the liquid crystal display of thefirst embodiment of the present invention except a pixel electrode 182and an alignment film 190, and thus, the repeated description thereofwill not be given and only differences will now be described.

Referring to FIGS. 11 and 12, the pixel electrode 182 electricallyconnected to a drain electrode 166 via a contact hole 177 is disposed ona passivation layer 170. The pixel electrode 182 is disposed in a pixelarea defined by intersections between gate lines 122 and data lines 162.For example, the pixel electrode 182 may be made of a transparentconductive material such as ITO or IZO.

Alignment film 190 is disposed on a substrate 110 having thereon thepixel electrode 182. Alignment film 190 is a horizontal alignment filmthat allows liquid crystal molecules 310 of a liquid crystal layer 300to be aligned horizontally with respect to the surface of the substrate110 in a voltage-off state. For example, the alignment film may be analignment film that allows the liquid crystal molecules 310 to have apretilt angle of 0.5 to 3 degrees. The alignment film is rubbed so thatthe liquid crystal molecules 310 of the liquid crystal layer 300 arealigned at an angle of α with respect to openings 270 a of a commonelectrode 270 as will be described later in a voltage-off state. Theangle of α may depend upon set optical properties of the LCD and may bean arbitrary angle except 0 and 90 degrees, for example, an angle in therange between 60 and 85 degrees.

A second plate 200 of the liquid crystal display of the third embodimentis the same as the second plate 200 of the liquid crystal display of thefirst embodiment of the present invention except common electrode 270and an alignment film 280, and thus, the repeated description thereofwill not be given and only differences will now be described.

Referring to FIGS. 11 and 12, common electrode 270 including a pluralityof the openings 270 a and a plurality of common electrode portions 270 bis disposed on an overcoat layer 250. For example, the openings 270 a ofcommon electrode 270 may be formed in a predetermined stripe shape to beparallel to the longer side of the pixel area. At this time, a width ofeach opening 270 a and a width of each common electrode pattern 270 bbetween the openings 270 a, i.e., a distance between the openings 270 aare determined by the optical properties of a liquid crystal display.For example, the width of each opening 270 a may be a range fromapproximately 4 to 14 μm, and the distance between the openings 270 amay be 6 μm or less. For example, when the width of each opening 270 ais 11 μm, the distance between the openings 270 a may be 4 μm. Commonelectrode 270 may be made of a transparent conductive oxide materialsuch as ITO or IZO.

As described above, alignment film 280 is disposed on a substrate 210having thereon common electrode 270. Alignment film 280 is a horizontalalignment film that allows the liquid crystal molecules 310 to bealigned horizontally with respect to the surface of substrate 210 in avoltage-off state. For example, alignment film 280 may be an alignmentfilm that allows the liquid crystal molecules 310 to have a pretiltangle of 0.5 to 3 degrees. The alignment film is rubbed so that theliquid crystal molecules 310 are aligned at an angle of α with respectto the openings 270 a in a voltage-off state. At this time, the rubbingdirection of the alignment film, together with the rubbing direction ofthe alignment 280 film of the first plate 100, forms an angle of 180degrees.

Next, referring to FIGS. 12 through 15, the arrangement of the liquidcrystal molecules 310 in the on/off state of a thin film transistor ofthe liquid crystal display according to the third embodiment will now bedescribed. FIGS. 13 and 14 are respectively schematic plan and sectionalviews illustrating the arrangement of liquid crystal molecules when athin film transistor of the liquid crystal display according to thethird embodiment of the present invention is in an “OFF” state, and FIG.15 is a schematic sectional view illustrating the arrangement of liquidcrystal molecules when a thin film transistor of the liquid crystaldisplay according to the third embodiment of the present invention is inan “ON” state.

First, referring to FIGS. 12 through 14, with respect to the arrangementof the liquid crystal molecules 310 in an “OFF” state thin filmtransistor, the liquid crystal molecules 310 between the pixel electrode182 formed in a pixel area and the overlying common electrode 270including a plurality of the openings 270 a parallel to the longer sideof the pixel area are aligned parallel to the rubbing direction of thehorizontal alignment films so that their long axes are inclined at anangle of 0.5 to 3 degrees with respect to the surfaces of the substrates110 and 210. For example, when the alignment films 190 and 280 of thefirst and second substrates 110 and 210 are rubbed in oppositedirections such that they have a tilt angle of 60° to 85° with respectto the opening 270 a, the long axes of the liquid crystal molecules 310are arranged at a tilt angle (α) of approximately 60 to approximately85° with respect to the opening 270 a.

Next, referring to FIGS. 12 and 15, with respect to the arrangement ofthe liquid crystal molecules 310 in an “ON” state thin film transistor,when the thin film transistor is turned-on and an image signal isapplied to the pixel electrode 182, an electric field is generatedbetween the first plate 100 and the second plate 200. At this time, inportions of the pixel electrode 182 corresponding to central portions ofthe common electrode portions 270 b interposed between the openings 270a of common electrode 270, there is generated a vertical electric fielddirecting toward the central portions of the common electrode portions270 b. On the other hand, a horizontal electric field which is notdirected to common electrode 270 but is converged is generated inportions of the pixel electrode 182 corresponding to the openings 270 a.The liquid crystal molecules 310 adjacent to the alignment films 190 and280 maintain their original alignments, whereas the liquid crystalmolecules 310 disposed in the central area of the liquid crystal layer300 are rotated so that their long axes are aligned vertically withrespect to an applied electric field due to the negative dielectricanisotropy. At this time, the liquid crystal molecules 310 are uniformlyrotated in the same direction based on a tilted angle created by rubbingof the alignment films 190 and 280.

In the liquid crystal display according to the above-describedembodiment, common electrode 270 has a plurality of the openings 270 ahaving a predetermined shape, whereas the pixel electrode 182 formed inthe pixel area is not subjected to patterning. Even though the pixelelectrode 182 is not subjected to patterning, the liquid crystal displayof this embodiment shows transmittance comparable to a PVA mode, likethe liquid crystal display of the first embodiment of the presentinvention. Also, since the pixel electrode 182 is not subjected topatterning, there is no misalignment between the pixel electrode 182 ofthe first plate 100 and common electrode 270 of the second plate 200,thereby causing no electric field distortion. Furthermore, an overlaparea between the pixel electrode 182 and common electrode 270 isreduced, thereby leading to low liquid crystal capacitance. Stillfurthermore, since the liquid crystal molecules 310 are tilted at apredetermined angle with respect to the openings 270 a of commonelectrode 270 in a voltage-off state, they can be uniformly rotated inthe same direction in a voltage-on state. Therefore, the liquid crystaldisplay of this embodiment is free from textures that are caused betweenliquid crystal molecules rotating in different directions, therebyleading to no abnormal domains. In addition, the liquid crystal displayof this embodiment shows maximal transmittance compared to anotherliquid crystal displays using liquid crystal molecules with higherdielectric anisotropy and the same voltage, and the in-plane movement ofthe directors of the liquid crystal molecules 310 increases, therebyensuring better visibility.

Hereinafter, a liquid crystal display according to a fourth embodimentof the present invention will be described with reference to FIGS. 16and 17. FIG. 16 is a layout of a liquid crystal display according to thefourth embodiment of the present invention, and FIG. 17 is a sectionalview taken along a line XVI-XVI′ of FIG. 16.

The liquid crystal display of this embodiment is the same as the liquidcrystal display including the openings 270 a of common electrode 270parallel to the longer side of the pixel area according to the previousembodiment except that an alignment film (190) of a first plate 100 andan alignment film 280 of a second plate 200 are rubbed at an angle of 90degrees with respect to the longer side of a pixel area under thecondition that the rubbing direction of alignment film 190 of the firstplate 100 and the rubbing direction of alignment film 280 of the secondplate 200 form an angle of 180 degrees, and openings 270 a of a commonelectrode 270 are formed parallel to each other in a state in which theyare inclined at a predetermined angle, e.g., an angle from 60 to 85degrees, with respect to the rubbing direction of alignment film 280 ofthe second plate 200. Thus, the repeated descriptions will be omitted.

Next, the liquid crystal molecule arrangement in the on/off state of athin film transistor of the liquid crystal display according to theillustrative embodiment will now be described with reference to FIGS. 17through 20. FIGS. 18 and 19 are respectively schematic plan andsectional views illustrating the arrangement of liquid crystal moleculeswhen a thin film transistor of the liquid crystal display according tothe fourth embodiment of the present invention is in an “OFF” state, andFIG. 20 is a schematic sectional view illustrating the arrangement ofliquid crystal molecules when a thin film transistor of the liquidcrystal display according to the fourth embodiment of the presentinvention is in an “ON” state.

First, referring to FIGS. 17 through 19, with respect to the liquidcrystal molecule arrangement in an “OFF” state thin film transistor,liquid crystal molecules 310 between a pixel electrode 180 formed in thepixel area, and common electrode 270 including the openings 270 a whichare parallel to each other and inclined at a predetermined angle, e.g.,at an angle of 60 to 85 degrees with respect to the rubbing direction ofalignment film 280 of the second plate 200 rubbed at an angle of 90degrees with respect to the longer side of the pixel area, are alignedparallel to the rubbing direction of the horizontal alignment films in astate in which their long axes are inclined at a pretilt angle of 0.5 to3 degrees with respect to the surfaces of first and second substrates110 and 210. That is, the long axes of the liquid crystal molecules 310are arranged at an angle of approximately 90° with respect to a longerside of the pixel area. Consequently, the long axes of the liquidcrystal molecules 310 are arranged at a tilt angle (α) of approximately60 to approximately 85° with respect to the sub electrode 182 a.

Next, referring to FIGS. 17 and 20, with respect to the arrangement ofthe liquid crystal molecules 310 in an “ON” state thin film transistor,when the thin film transistor is turned-on and an image signal isapplied to the pixel electrode 182, an electric field is generatedbetween the first plate 100 and the second plate 200. At this time, inportions of the pixel electrode 182 corresponding to central portions ofthe common electrode portions 270 b between the openings 270 a of commonelectrode 270 a, there is generated a vertical electric field directingtoward the central portions of the common electrode portions 270 b. Onthe other hand, a horizontal electric field which is not directed to thecommon electrode portions 270 b but is converged is generated inportions of the pixel electrode 182 corresponding to the openings 270 a.The liquid crystal molecules 310 adjacent to the alignment films (190and 280 maintain their original alignments, whereas the liquid crystalmolecules 310 disposed in the central area of the liquid crystal layer300 are rotated so that their long axes are aligned vertically withrespect to an applied electric field due to the negative dielectricanisotropy. At this time, the liquid crystal molecules 310 are uniformlyrotated in the same direction based on a tilted angle created by rubbingof the alignment films (190 and 280.

The liquid crystal display according to the illustrative embodimentshows transmittance comparable to a PVA mode, like the liquid crystaldisplay including the openings 270 a parallel to the longer side of thepixel area according to the previous embodiment of the presentinvention. Also, since the pixel electrode 182 is not subjected topatterning, there is no misalignment between the pixel electrode 182 ofthe first plate 100 and common electrode 270 of the second plate 200,thereby causing no electric field distortion. Furthermore, an overlaparea between the pixel electrode 182 and common electrode 270 isreduced, thereby leading to low liquid crystal capacitance. Stillfurthermore, since the liquid crystal molecules 310 are tilted at apredetermined angle with respect to the openings 270 a of commonelectrode 270 in a voltage-off state, they can be uniformly rotated inthe same direction in a voltage-on state. Therefore, the liquid crystaldisplay of this embodiment is free from spurious patterns called“textures” that are caused between liquid crystal molecules rotating indifferent directions, thereby leading to no abnormal domains. Inaddition, the liquid crystal display of this embodiment shows maximaltransmittance compared to other liquid crystal displays using liquidcrystal molecules with higher dielectric anisotropy and the samevoltage. Also, the in-plane movement directions of the liquid crystalmolecules 310 increases, thereby ensuring better visibility.

Hereinafter, the present invention will be described more specificallywith reference to experimental example. The following experimentalexample is for illustrative purposes and is not intended to limit thescope of the invention.

First, the characteristics of a liquid crystal display according to anembodiment of the present invention were evaluated through simulation,and the maximum transmittance of the liquid crystal display obtainedthrough the simulation is presented in Table 1 below. In Table 1, w is awidth of each sub-electrode of a pixel electrode, L is a distancebetween sub-electrodes of a pixel electrode, D is a cell gap, Δn isbirefringence, Δε is dielectric anisotropy, and Φ is an angle between 20sub-electrodes of a pixel electrode and a rubbing direction. Theequipotential lines formed in the “ON” state of thin film transistors ofthe liquid crystal display of this experimental example arediagrammatically illustrated in FIG. 21. FIG. 21 illustrates theequipotential lines formed between stripe-shaped sub-electrodes 182 aformed on a first substrate 110 of a first plate 100 and a commonelectrode 270 formed on a second substrate 210 of a second plate 200,and the arrangement of liquid crystal molecules 310 having negativedielectric anisotropy in a liquid crystal display according to anembodiment of the present invention. TABLE 1 LCD CharacteristicsTransmittance w L D Δn Δ∈ φ (%) Experimental 4 11 5.2 0.0800 −6 80 42.29Example

As shown in Table 1 and FIG. 21, the transmittance of the liquid crystaldisplay according to this experimental example was approximately 42.29%which was equal to or greater than that of a PVA-mode liquid crystaldisplay.

As described above, a liquid crystal display according to the presentinvention minimizes an overlap area between field-generating electrodesand has the structure capable of allowing liquid crystal molecules to bealigned horizontally and generating a horizontal electric field, therebyincreasing visibility and transmittance. Furthermore, since any one offield-generating electrodes is patterned, less electrostatic problemsare caused. There, there is no need to form a conductive polarizationplate, thereby increasing process efficiency. Also, there is nomisalignment between a first plate and a second plate, thereby causingno electric field distortion.

As hereinabove described, the alignment layer aligns liquid crystalmolecules in a predetermined direction and is advantageously made of apolyimide or polyamide acid. The “rubbing” is performed by rubbing thealignment layer in a specific direction using a fabric. When thealignment layer is rubbed, the liquid crystal molecules are arranged inthe specific direction. Those skilled in the art will understand thekinds of materials of which the alignment layer may be made and how therubbing is performed. The present invention is characterized in that thecommon electrode need not be patterned and the liquid crystal moleculesare initially aligned to have a predetermined angle with respect to thesub electrode 182 using a horizontal alignment layer.

In concluding the detailed description, those skilled in the art willappreciate that many variations and modifications can be made to thepreferred embodiments without substantially departing from theprinciples of the present invention. Therefore, the disclosed preferredembodiments of the invention are used in a generic and descriptive senseonly and not for purposes of limitation.

1. A liquid crystal display comprising: a first plate having a firstfield-generating electrode, disposed in a pixel area of on insulatingsubstrate, comprising a plurality of sub-electrodes which are separatedfrom each other by a predetermined distance and arranged parallel toeach other, and a connecting electrode electrically connecting thesub-electrodes, and a first alignment film covering the firstfield-generating electrode said first alignment film having been rubbedin a first direction; a second plate having a second field-generatingelectrode disposed on an insulating substrate, and a second alignmentfilm covering the second field-generating electrode said secondalignment film having been rubbed in a second direction; and a liquidcrystal layer interposed between the first plate and the second plate.2. The liquid crystal display of claim 1, wherein a width of each of thesub-electrodes is 6 μm or less.
 3. The liquid crystal display of claim1, wherein a distance between the sub-electrodes is in a range between 4and 14 μm.
 4. The liquid crystal display of claim 1, wherein the firstand second alignment films are horizontal-alignment films.
 5. The liquidcrystal display of claim 1, wherein the pre-tilt angle of liquid crystalmolecules constituting the liquid crystal layer is in a range between0.5 and 3 degrees.
 6. The liquid crystal display of claim 1, whereinliquid crystal molecules constituting the liquid crystal layer havenegative dielectric anisotropy.
 7. The liquid crystal display of claim1, wherein the first direction and the second direction form an angle of180 degrees.
 8. The liquid crystal display of claim 1, wherein thesub-electrodes and the first direction form an angle of 60 to 85degrees.
 9. A liquid crystal display comprising: a first plate having afirst field-generating electrode disposed in a pixel area on aninsulating substrate; a first alignment film covering the firstfield-generating electrode, said first alignment film having been rubbedin a first direction; a second plate having a second field-generatingelectrode disposed on an insulating substrate, said secondfield-generating electrode having a plurality of openings formedparallel to each other in an area corresponding to the pixel area of thefirst plate; a second alignment film covering the secondfield-generating electrode, said second alignment film having beenrubbed in a second direction; and a liquid crystal layer interposedbetween the first plate and the second plate.
 10. The liquid crystaldisplay of claim 9, wherein a distance between the openings is 6 μm orless.
 11. The liquid crystal display of claim 9, wherein a width of eachof the openings is in a range between 4 and 14 μm.
 12. The liquidcrystal display of claim 9, wherein the first and second alignment filmsare horizontal-alignment films.
 13. The liquid crystal display of claim9, wherein the pre-tilt angle of liquid crystal molecules constitutingthe liquid crystal layer is in a range between 0.5 and 3 degrees. 14.The liquid crystal display of claim 9, wherein liquid crystal moleculesconstituting the liquid crystal layer have negative dielectricanisotropy.
 15. The liquid crystal display of claim 9, wherein the firstdirection and the second direction form an angle of 180 degrees.
 16. Theliquid crystal display of claim 9, wherein the openings and the seconddirection form an angle of 60 to 85 degrees.